Grinding machine

ABSTRACT

This invention relates to a grinding machine making use of a closed-loop control of grinding force. In the control system, data on wheel size and wheel dullness are used to continuously determine grinding rate.

United States Patent Hahn et al. 1 1 Oct. 21, 1975 1 1 GRINDING MACHINE175] Inventors: Robert S. Hahn, Norlhhorn; H

Richard 1. Lindsay, Marlboro, holh UNHH) 51A 1 [3S PAIBNIS 01 Mass.3,274,738 9/1966 Kuniholm 51/165 R 3,503,158 3/1970 Rohillard c1211.51/1658 1731 f 'j M'lacmn'fleald 3,524,235 11/1970 R1111 51/13 1-: x(impflralmn, Worcester, 3,534,509 10 1970 111113111161 61. 51/165913,535,828 10/1970 Ware c1211. ..51/1(15,8 1974 3,570,189 3/1971 Kcding51/1345 R 121] Appl. No.1 465,237 3,601,930 8/1971 R0hi11z1rd 51/1658Reluted Applica i Dam Primary lz'xamincn-Hunfld D. Whitehead [63](unlmuatmn 01 Sun N01 285,628, Sept. 1, 1972, Attorney, Agent, or pi N SBl d u; (j

which is a continuation of Scr. No. 94,389, Dec. 2, Blodgeu 1970,abandoned 57 ABSTRACT 152] US. Cl. ..51/165.77;51/134.5;51/165.87;

SH165 92 lhls 1nvcnt10n relates to a grlndlng muchmc makmg 2 I use of aclosed-loop control of grinding force. In the [51] lnLCl. ..B24B49/ l0 dh d h Id H [58] Field 61 Search 51/165 R, 165.71, 165.77, W cc u 5 H658,1658246586, 165946592 are used to contmuously determmc grmdmg ram 139,134.5 1 Claim, 2 Drawing Figures COMgtNsgTION 1 NmcA'noN MODULATiONWNCELSiZE .4G 44 ATTENJATOR \ND1CAT1ON 73 42 l4l 94 55 56 32 33 34 35 35Fon'cz men FORCE R- STEP? SHAPiNG REFE MOTOR mfg-Ts ATTENUATOR NETWORKDRNE lu'rznneumn:

FORCE v ATTENUKTOR 17 1b 525 i 55 LOW FORCE 5 DAMPER ATTENUATOR 1 Z4 6TRANSDUCER FORCE. 1 1 FINAL FGICE 3 AMPL HER TRANSDUCER GRNDNBATTENUATOR PROCESS 2a 14 13 41 WHEEL. Fm

DIAPH DULLNESS as 21 MGM CYUNDER 11 HYDRAUUC 1 PRESSURE r z GRINDINGMACHINE This is a continuation of application Ser. No. 285,628 filedSept. l, 1972, which is a continuation of application Ser. No. 94,389filed Dec. 2, 1970.

BACKGROUND OF THE INVENTION In the operation of a grinding machine,there are several advantages to operating in such a manner that theforce is controlled at a predetermined value and the rate of feed isallowed to vary uncontrollably. However, there are also attendantdisadvantages, particularly where the machine used is an internalgrinding machine; in that case, the abrasive wheel is mounted on acantilevered spindle and is subject to considerable bending. There areso many variables that enter into the determination of the actualgrinding force between the wheel and the workpiece that all kinds ofproblems are presented. The simplest method of controlling the force isto use a hydraulic cylinder for cross-feed and to control the oilpressure in the cylinder. In a rough way (assuming that there is nofriction in the crossslide), the force between the abrasive wheel andthe workpiece is proportional to the pressure of the oil'in thecylinder. However, as a practical matter, a number of variables enterinto the picture that destroy this simple relationship. The sharpness orcutting ability of a wheel can vary from time to time and from wheel towheel. The nature of the material being ground also varies. The forcechanges when the size of the wheel changes as it is dressed down fromone grinding cycle to the next. Variation in force between the abrasivewheel and the workpiece can cause variation in taper in the finishedground surface and so on. These and other difficulties experienced withthe prior art devices have been obviated in a novel manner by thepresent invention.

It is, therefore, an outstanding object of the invention to provide agrinding machine having a control for maintaining the force between theabrasive wheel and the workpiece at a constant perdetermined value.

Another object of this invention is the provision of an internalgrinding machine in which taper and surface finish can be maintained ata predetermined value.

A further object of the present invention is the provision of a grindingmachine having a closed-loop force control which is relatively simple inconstruction and operation.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION In general, the invention has "to do with agrinding machine having a base, having a table carrying a wheelhead witha spindle and abrasive'avheel mounted on the base, and having a tablecarrying a workhead with a workpiece mounted on the base. Feed means ispro vided to bring about relative movement between the tablestransversely of the spindle to cause a grinding action between the wheeland the workpiece. A gage is provided for measuring the instantaneousforce between the wheel and the workpiece and a feed-back controlreceives a signal from the gage and is operative, when the signal variesfrom a predetermined value; to adjust the feed means.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention,however, may be best understood by reference to one of its structuralforms, as illustrated by the accompanying drawings, in which:

FIG. 1 is a schematic view of a grinding machine and its controls builtin accordance with the principles of the present invention, and

FIG. 2 is a schematic view of the operative portions of the grindingmachine.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 it can be seen thatthe grinding machine, indicated generally by the reference numeral in 10includes a feed cylinder 11 which receives a constant hydraulic pressurefrom a source 112. The feed cylinder 1 1 is operative on the grindingprocess 13, as indicated by a line 14. Thegrinding process is alsoaffected by the system spring constant K indicated by the box 15. Thespring constant K is shown in FIG. 2 as the combined spring constant ofthe machine and constitutes the sum of Kw, Ks, and Kg. For the purposeof demonstrating control logic, a line 16 leads from the box 15 to asignal junction 17 to show that the grinding process 13 is affected bothby the system spring constant and by the force from the feed cylinder11. A damper box 18 is connected to the grinding process 13 and to thejunction 17 to show the manner in which the damper effects the grindingprocess.

A line 19 extends from the source 12 to a diaphragmtype force measuringdevice 21 of the type shown in the US. Pat. No. 3,618,269, dated Nov. 9,1971. This device contains a diaphragm which receives the same oilpressure as the feed cylinder 11, the other side of the diaphragmreceiving the full grinding force of the machine. A strain gage mountedon the diaphragm gives a signal indicative of the grinding force andthis appears on the line 22 and is applied to one inlet of the junction23. The other inlet receives a signal from the system K box 15 through aline 24. The combined effects of the grinding process force and thesignal from the diaphragm 21 is felt by the force transducer 25 which isamplified in the amplifier 26 resulting in a signal on a line 27. Thissignal passes along a line 28 to a wheel dullness indicator 29 and alonga line 31 to a junction 32.

The signal from the junction 32 is introduced into an error signalamplifier 33 whose output signal is introduced to a pulse generator 34.The ouput of the pulse generator 34 appears on a line 35 leading to astepping motor drive 36 which operates through a gear train and ballscrew apparatus 37 which, in turn, operates through a junction 38 whosesignal is felt in the system K box 15.

The output line 35 of the pulse generator 34 is connected by a line 39which is connected to the input of the wheel dullness indicator 29. Theoutput of this indicator appears on a line 41 which is connected to ajunction 42. Also connected to the junction 42 is a force reference box43 and a line 44 leading from a modulation attenuator 45. Thisattenuator receives a signal from a wheel size indicator 46 which, inturn, receives a signal from a compensation slide indicator 47. Thewheel size indicator 46 is of the type shown and described in the patentapplication of Robillard Ser. No.

877,092, filed Nov. 17, 1969, now US. Pat. No.

3,601,930 dated Aug. 31, 1971. The wheel dullness indicator 29 is of thetype shown and described in the US. Pat. No. 3,745,710, dated July 17,1973.

The output of the junction 42 appears on a line 48 which is introducedinto a high force attenuator 49, an intermediate force attenuator 51, alow force attenua tor 52, and a final force attenuator 53. The highforce attenuator 49 feeds into an R-C shaping network 54 and from therethrough a normally closed contactor 55 and a normally open contactor 56(which is always closed during grinding) into the junction 32. Theintermediate force attenuator 51 is connected through a normally closedcontactor 57 and a normally open contactor 58 to a point between thecontactors 55 and 56. The low force attenuator 52 is connected through anormally closed contactor 59 and a normally open contactor 61 to a pointbetween the contactors 57 and 58. The final force attenuator 53 isconnected through a normally open contactor 62 to a point between thecontactors 59 and 61'. The contactors 55 and 58 form part of the samerelay and, therefore, change condition at the same time. Similarly, thecontactors 57 and 61 form part of the same relay as do the contactors 59and 62.

FIG. 2 shows somewhat schematically a grinding machine with which thecontrol of FIG. 1 is used. It can be seen that the wheelhead table 63has a mass m and is pressed rearwardly by the feed cylinder 73 as ittravels over 18. base 64. The travel is damped by damper 18 The tablecarries a spindle 65 with an abrasive wheel 66 mounted thereon. Thewheel operates on the surface of a workpiece 67 which, in turn, ismounted on the base 64. The table 63 has a retractable stop 68 operatedby a stepping motor 69. This stop engages on occasion the diaphragm 21mounted on the compensation slide 70. The compensation slide is movedrelative to the base 64 by means of a screw 71 operated by a steppingmotor 72. The same pressure oil that appears behind the diaphragm 21also operates the feed cylinder 73.

It is obvious that the minor changes may be made in the form andconstruction of the invention without de parting from the materialspirit thereof. It is not, however, desired to confine the invention tothe exact from herein shown and described, but it is desired to includeall such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent l. A grinding machine for producinga surface of revolution on a workpiece, comprising:

a. a base,

b. a table carrying a wheelhead with a spindle and abrasive wheelmounted on the base,

c. means for mounting the workpiece on the base,

(1. feed means to bring about relative movement between the tables andthe base transversely of the spindle to bring about an instantaneousforce between the wheel and the workpiece to cause a grinding actionbetween the wheel and the workpiece,

e. a gage for measuring the instantaneous force between the wheel andthe workpiece,

f. a sensing system adapted to determine the wheel size and the wheeldullness and to generate signals indicative of these physicalcharacteristics, and

g. a feed-back control receiving a combined signal from the gage and thesensing system, and operative, when the combined signal varies from apredetermined value, to adjust the feed means.

1. A grinding machine for producing a surface of revolution on aworkpiece, comprising: a. a base, b. a table carrying a wheelhead with aspindle and abrasive wheel mounted on the base, c. means for mountingthe workpiece on the base, d. feed means to bring about relativemovement between the tables and the base transversely of the spindle tobring about an instantaneous force between the wheel and the workpieceto cause a grinding action between the wheel and the workpiece, e. agage for measuring the instantaneous force between the wheel and theworkpiece, f. a sensing system adapted to determine the wheel size andthe wheel dullness and to generate signals indicative of these physicalcharacteristics, and g. a feed-back control receiving a combined signalfrom the gage and the sensing system, and operative, when the combinedsignal varies from a predetermined value, to adjust the feed means.